Upscaling Evapotranspiration with Parsimonious Models in a North Carolina Vineyard

Christian Dold,Gill Giese,Joshua Heitman,John Havlin,Adam Howard,Tom Sauer

doi:10.3390/agronomy9030152

Abstract

Water stress can positively or negatively impact grape yield and yield quality, and there is a need for wine growers to accurately regulate water use. In a four-year study (2010–2013), energy balance fluxes were measured with an eddy-covariance (EC) system in a North Carolina vineyard (Vitis vinifera cv. Chardonnay), and evapotranspiration (ET) and the Crop Water Stress Index (CWSI) calculated. A multiple linear regression model was developed to upscale ET using air temperature (Ta), vapor pressure deficit (VPD), and Landsat-derived Land Surface Temperature (LST) and Enhanced Vegetation Index (EVI). Daily ET reached values of up to 7.7 mm day−1, and the annual ET was 752 ± 59 mm, as measured with the EC system. The grapevine CWSI was between 0.53–0.85, which indicated moderate water stress levels. Median vineyard EVI was between 0.22 and 0.72, and the EVI range (max–min) within the vineyard was 0.18. The empirical models explained 75%–84% of the variation in ET, and all parameters had a positive linear relationship to ET. The Root Mean Square Error (RMSE) was 0.52–0.62 mm. This study presents easily applicable approaches to analyzing water dynamics and ET. This may help wine growers to cost-effectively quantify water use in vineyards.

Highlights

Quantifying water use in a vineyard is critical because plant available water in the root zone determines yield quantity and quality
Water use in vineyards can be regulated by estimating the daily actual evapotranspiration (ET), i.e., the amount of water transpired by the crop, or evaporated from the soil and exposed surfaces
Was the use of the reference evapotranspiration (ET0 ) multiplied with a crop coefficient [21], of which the former was calculated from meteorological data, and the latter was substituted by a satellite-derived vegetation index (VI) [14,22]

Summary

Introduction

Quantifying water use in a vineyard is critical because plant available water in the root zone determines yield quantity and quality. Volumetric soil water content (VWC) as a predictor of ET, and measured with EC stations, was used to upscale ET in the North American monsoon region [20] Another way to estimate ET was the use of the reference evapotranspiration (ET0 ) multiplied with a crop coefficient (kc) [21], of which the former was calculated from meteorological data, and the latter was substituted by a satellite-derived vegetation index (VI) [14,22]. Landsat imagery provides EVI and LST products at a 30 × 30 m resolution, which would allow ET to be estimated on a subfield level using parsimonious regression models In this four-year study, actual ET and CWSI were estimated in a commercial vineyard in NC, USA, using the EC method as a comparison to quantify associated ET. This study’s aim was to monitor the water dynamics and quantify ET, and to eventually upscale ET from sub-field to vineyard level by developing a parsimonious empirical model using micro-meteorological data and Landsat 7 imagery

Study Site

Eddy Covariance System

Statistical Analysis and Data Preparation

Results

Modeled

Discussion